The present disclosure relates to a gas turbine engine, and more particularly to a turbofan engine having a variable area fan nozzle (VAFN) with a VAFN cowl which increases a flutter margin.
Gas turbine engines which have an engine cycle modulated with a variable area fan nozzle (VAFN) provide a smaller fan exit nozzle during cruise conditions and a larger fan exit nozzle during take-off and landing conditions.
A design requirement for the VAFN is to maintain structural integrity throughout the flight envelope of the aircraft. Due to flow turbulence and mechanical vibration, the VAFN may be subject to both tonal and broadband aerodynamic loads that cause the nozzle to elastically deflect from a mean position.